The FDLR is a descendant of Rwandan Hutu extremist groups that fled into the Democratic Republic of Congo after carrying out the 1994 Tutsi genocide in Rwanda.
The DRC is regularly accused of working alongside the mainly Hutu FDLR in its fight against Tutsi-led M23 rebels, in turbulent eastern Congo.
In a video statement on Monday evening, Congolese army spokesman Sylvain Ekenge said that all soldiers regardless of rank are “strictly and unconditionally forbidden” to maintain contacts with the FDLR.
“Any person contravening this instruction will be placed under arrest and will suffer the rigour of the law,” he said, adding that there would be “zero tolerance”.
According to independent UN experts, Congolese soldiers have cooperated with FDLR fighters against the M23.
A Tutsi-led group, the M23 has seized swathes of eastern DRC since launching an offensive in late 2021 and driven over one million people from their homes.
The M23 is backed by Rwanda, according to UN experts as well as several Western states including the United States and France.
Both the M23 and the Rwandan government often accuse the DRC of working with the FDLR.
An AFP team also witnessed Congolese soldiers cooperating with FDLR fighters in late October, in the town of Bambo in North Kivu province, as the M23 was advancing.
The Congolese army statement forbidding cooperation with the FDLR follows a recent visit to both the DRC and Rwanda by US intelligence chief Avril Haines.
The White House said on Tuesday that she had secured promises from leaders of both countries to de-escalate tensions.